The present invention relates generally to braking apparatus for use in motor vehicles, and more particularly to such a braking apparatus for controlling the slippage of a wheel of the motor vehicle.
Such a braking apparatus is known as exemplified by description in the Japanese Patent Provisional Publication No. 1-254460 where there is provided a braking hydraulic pressure supply source for applying a braking force to a wheel of a motor vehicle when slip occurs at the time of driving of the wheel. This braking hydraulic pressure supply source comprises a pump coupled to a reservoir tank, an accumulator connected to the discharge side of the pump for accumulating a high-pressure braking liquid, and a pressure switch for detecting the pressure within the accumulator. The pump is driven in response to a detection signal of the pressure switch so as to keep the pressure within the accumulator in a predetermined range. However, one of important problem is that such a braking hydraulic pressure supply source complicates the structure of the braking apparatus and increases the weight of the braking apparatus, and another problem is that there is the possibility that the accumulator deteriorates the braking performance because gas is mixed in the braking hydraulic pressure passage. In addition, when the drive slip occurs, the braking liquid having a pressure higher than the pressure within the accumulator is supplied into a wheel cylinder of the wheel, thereby generating a large working sound because the pressure-increasing speed is too high.
The Japanese Patent provisional Publication No. 2-18150 discloses a technique to reduce the size and weight of the braking apparatus by using a self-priming pump for preventing the drive slip of the wheel. However, this self-priming pump is very restricted in its installing position because the suction resistance of the self-priming pump increases in the case that the distance between the self-priming pump and the reservoir tank is long. Moreover, if some trouble occurs in the self-priming pump, difficulty is encountered to perform both the wheel braking operation and drive slip preventing operation.